CorpusHuman Anatomy
SkeletalJoint

Atlanto-axial joint

Articulatio atlantoaxialis

Also known as: AA joint, no joint, median atlanto-axial joint

Three synovial joints between the atlas and axis — a median pivot joint around the dens and two lateral plane joints — that allow rotation of the head ("no" movement).

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Overview

The median atlanto-axial joint is a pivot joint: the dens of the axis rotates within a ring formed anteriorly by the anterior arch of the atlas and posteriorly by the strong transverse ligament of the atlas, with a synovial cavity on each side of the dens. The two lateral atlanto-axial joints are plane joints between the inferior facets of the atlas and the superior facets of the axis. Together they permit rotation of the atlas and skull on the axis of ≈40–45° to each side — about half of all cervical rotation.

The transverse ligament has superior and inferior longitudinal bands (to the foramen magnum and the body of the axis), forming the cruciform ligament. The alar ligaments, running from the sides of the dens to the medial margins of the occipital condyles, check excessive rotation; the apical ligament joins the dens tip to the foramen magnum; the tectorial membrane (upward continuation of the posterior longitudinal ligament) covers these ligaments posteriorly. There is no intervertebral disc between C1 and C2.

Location

Between the first and second cervical vertebrae.

Parts & subdivisions

  1. Median atlanto-axial joint
    Pivot joint between the dens, the anterior arch of the atlas and the transverse ligament.
  2. Lateral atlanto-axial joints
    Paired plane joints between the lateral masses of C1 and C2.
  3. Transverse ligament of the atlas
    Holds the dens against the anterior arch; part of the cruciform ligament.
  4. Alar ligaments
    Dens to occipital condyles; limit rotation.

Anatomy

Innervation

C2 spinal nerve.

Articulations

Dens ↔ anterior arch of atlas and transverse ligament; lateral masses of atlas ↔ superior facets of axis.

Ligaments

Cruciform (transverse ligament + longitudinal bands), alar, apical, tectorial membrane, anterior atlanto-axial membrane, ligamentum flavum.

Function

  • Rotation of the head (shaking the head "no")
  • Keeps the dens away from the spinal cord

Clinical significance

Atlanto-axial subluxation

Rupture or laxity of the transverse ligament (rheumatoid arthritis, Down syndrome, trauma, retropharyngeal infection — Grisel syndrome) lets the dens move back into the vertebral canal, risking cervical myelopathy or sudden death; check flexion–extension X-rays before anaesthesia in RA.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.